With the arrival of digital making it possible to process ever bigger information throughputs, a problem of available frequency bandwidth for the broadcasting of multimedia applications over the airwaves is encountered. For a sufficient throughput, the trend is to rise in frequency towards the, as yet, free bands. Thus, new bidirectional radio systems have made their appearance in the millimetre bands. Known in particular is the MWS system (Multimedia Wireless System) which occupies 3 GHz of frequency band between 40.5 and 43.5 GHz. These fixed systems rely on a cellular deployment of the type used for mobile telephony (GSM). In order to avoid interference between cells, these systems use a pattern comprising an adequate number of cells, each cell of this pattern being differentiated from the others by its frequency band and also by the polarization used by the antennas. This allows maximum distancing between two subscribers using the same frequency and the same polarization and thus makes it possible to limit the risks of interference. Moreover, these systems being bidirectional, they can transmit in “full duplex” or simultaneous bidirectional mode. In this case, the subscriber side transmission or reception part must meet severe constraints regarding isolation between transmission and reception. Hence, an adequate frequency gap must be ensured between the up path and the down path in order to hone the implementation of the diplexer and limit the cost of the subscriber terminal. It is therefore necessary simultaneously to select two filters which will form the diplexer making it possible to isolate the transmission path and the reception path. The frequency gap being fixed by the constraints of implementation of the transmission/reception module, there are a number of transmission and reception filter pairs or RxTx filters allowing total coverage of the frequency plan required for deployment. To ensure correct deployment of a system of this type, it is therefore necessary to have several models of subscriber transmitter/receiver modules operating in several frequency bands. This multiplicity of configurations poses cost problems in the mass production of the subscriber terminal, this problem being all the more acute the bigger the frequency band to be shared.
One solution for avoiding having several versions of transmitter/receiver modules as a function of the desired frequency band consists in designing a transmitter/receiver module comprising all the filters covering the frequency plan, the choice of the filters being made by electronic switching with the aid of diodes. However, the use and the number of diodes required to implement the transmitter/receiver module tend to increase the cost of the terminal. Moreover, the switching circuits give rise to losses at millimetre frequencies and degrade the performance of the transmitter/receiver module. If one takes into account the fact that the selection of the frequency band and of the polarization of the signal will be done only once when installing the terminal at the subscriber's, the above solution appears to be much too complex and costly.